Initializing array to null but failing null comparison

Question

In the below code, my expectation is if list readerList.size = 0, headerLine should be null inside the method commonValidation(). But this is not the case, can anyone tell me why?

String[] headerLine = null;

if (readerList != null && readerList.size() != 0){
    headerLine = readerList.get(0);         
}

commonValidation(headerLine, logDTO, hrGroupName, feedFileName);

//method definition

public void commonValidation(String[] headerLine, TransactionLogDTO logDTO, String hrGroupName, String filename) throws PersistenceException, ServiceException, Exception {
    if ((headerLine == null) || (headerLine.length == 0)){
        logDTO.setGyr("R");

            String subject = MessageWrapper.getMessage("hr.mail.emptyfile.subject");
        String body = MessageWrapper.getMessage("hr.mail.emptyfile.body", filename);

            if (logDTO.getMessage() == null){
                logDTO.setMessage(body);
            }
            else{
                logDTO.setMessage(logDTO.getMessage() + ";" + body);
            }

        logDTO.setIsLogErrorMailSent(Boolean.TRUE);

        sendTransactionLogErrorReport(hrGroupName, subject, body);                  

        throw new Exception(body);
    }
}

have you checked that the readerList.size()? isn't 0 and readerList isn't null? Otherwise I don't see a problem. — Aske B.
– Aske B., Commented Sep 4, 2012 at 9:22
There is a logical error in this question. From accepted answer it becomes obvious that OP was not interested in "if A then B" violation, but in violation of "if B then A". — Jarekczek
– Jarekczek, Commented Sep 4, 2012 at 13:19
Sorry guys ,actually there was a nullpointer before the method "commonValidation" was called,which resulted in the above scenario.Seeing the answer below i actuall changed my implementation a bit in using existing value from arraylist rather than use a seperate array to capture the data from the list and then use it for validation.So i accepted the below answer.Sorry if i was wrong in accepting the answer. — ashwinsakthi
– ashwinsakthi, Commented Sep 4, 2012 at 15:25

Amit Deshpande · Accepted Answer · 2012-09-04 09:53:42Z

2

String[] headerLine = null; is this a member variable? if yes then make it method local variable.

Also

You can add null elements in ArrayList and size is increased.

    ArrayList<String[]> arrayList = new ArrayList<String[]>();
    arrayList.add(null);
    System.out.println(arrayList.size());

Will Print 1 not 0.

So check readerList.get(0) is null or not

Here is the source code of ArrayList add method

 410       public boolean add(E e) {
 411           ensureCapacityInternal(size + 1);  // Increments modCount!!
 412           elementData[size++] = e;
 413           return true;
 414       }

If you see there is no check of null so you will have to do it yourself :)

edited Sep 4, 2012 at 9:53

answered Sep 4, 2012 at 9:25

Amit Deshpande

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Comments

Jarekczek · Accepted Answer · 2012-09-04 09:40:34Z

0

But this is not the case, (...)

I don't believe. If readerList.size() == 0 headerLine does not change the value and remains null.

answered Sep 4, 2012 at 9:40

Jarekczek

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1 Comment

Aske B. Over a year ago

Unless of course another thread changes the value, or other code that the OP is leaving out.

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